Method of fabricating pliable polyfilamentous plastic strands

ABSTRACT

FABRICATION OF PLIABLE POLYFILAMENTOUS STRANDS BY IMPREGENATING THE STRAND WITH AN OIL OF LUBRICATING VISOSITY, HOT-STRECHING THE IMPREGENATED STRAND, REMOVING THE OIL OFLUBRICATING VISCOSITY, WATER-WASHING THE STRAND AND IMPREGNATING THE STRAND WHILE WET WITH INERT, POLYMERIC PARTICLES TO PROVIDE A POLYFILAMENTOUS STRAND OF IMPROVED SOFTNESS AND PIABILITY.

Aug. 21, 1973 D M ET AL 3,754,069

METHOD 01- FABRICATINQPLIABLE POLYFILAMENTOUS PLASTIC STRANDS OriginalFiled July 23, 1969 LEONARD D. KURTZ JOSEPH H. ADAMS I BY 07.36 QO /WATTORNEY 5 Qj INVENTOR United States Patent Ice 3 754 069 METHOD OFFABRICATING PLIABLE POLY- FILAMENTOUS PLASTIC STRANDS Joseph H. Adams,Vernon, Conn., and Leonard D. Kurtz,

Woodmere, N.Y., assignors to Sutures, Inc., Coventry, Conn.

Continuation of abandoned application Ser. No. 843,987,

July 23, 1969. This application Aug. 23, 1971, Ser. No. 174,142

Int. Cl. B29c 17/02; A611 17/00 U.S. Cl. 264-131 8 Claims ABSTRACT OFTHE DISCLOSURE This application is a continuation of Ser. No. 843,987,filed July 23, 1969, now abandoned.

This invention relates to an improvement in the fabrication of pliableplastic polyfilamentous strands such as pliable sutures.

Plastic strands, for example, braided or twisted polyethyleneterephthalate threads, have certain physical and chemical propertiessuperior to naturally occurring materials for many applications.Polyfilamentous polyethylene terephthalate threads, for example, aresuitable for use as surgical sutures because of the high tensilestrength and inertness thereof. However, the thread is very stiffrelative to, for example, silk of equal tensile strength and/ordimension and this lack of pliability causes the knottingcharacteristics of the thread to be quite poor for surgical use. To thisend, various methods have been disclosed in the art for modifying thelubricity and pliability of plastic threads such that the knottingproperties are similar to those of silk threads.

Moreover, to make the polyfilamentous strand suitable for use, includingsurgical use, it has been necessary to reduce the elasticity and memory(tendency to return to original length) of the plastic polyfilamentousstrand by hot-stretching the strand.

A method for providing a polyfilamentous plastic strand of improvedsoftness and pliability has been described in copending application Ser.No. 78,174 to Joseph H. Adams and Leonard D. Kurtz, filed Oct. 2, 1970,now abandoned. In accordance with that invention, a polyfilamentousplastic strand is first impregnated with an oil of lubricating viscosityand then hot-stretched while maintaining the strand at least at theheat-setting temperature thereof. The hotstretched strand is thenpermitted to cool and the impregnated strand is found to possess agreater pliability and softness than non-treated strands. In a preferredembodiment of that invention, the lubricating oil impregnant is removedas by solvent extraction after heat-stretching and the strand is thenwater-washed, dried and then impregnated with inert, polymeric particlessuch as Teflon. It has now been unexpectedly found that in thispreferred process for improving the softness and pliability ofpolyfilamentous strands, omission of the drying step provides a finalproduct of improved softness. Apparently, drying of the strand, afterwater-washing and before impregnation with the polymeric particles,causes some return of the stiffness originally found in the material.Consequently, when the material is subsequently impregnated with thepolymeric particles, no further softening is obtained; this small returnof stiffness persists and remains a permanent 3,754,069 Patented Aug.21, 1973 part of the product. If, however, after the water-wash step,the strand is impregnated with the polymeric particles before drying,there is no return of stitfness and the product remains dead soft.Furthermore, wetting and drying after impregnation, in accordance withthe process of this invention, does not cause return of stiliness.

Without being bound by any explanation or theory, we believe that thereturn of stiffness to the material is due to internal cohesions. If theindividual filaments in the polyfilamentous strand are permitted to dryagainst each other, internal attractions between the adjacent filamentsare probably being introduced causing a degree of stiffness. When thestrand is wet with water, however, water is interposed between filamentseliminating the cohesive effect. Then, when the strand is subsequentlyimpregnated with the polymeric particles, the latter interposes amechanical barrier between filaments preventing close contact and thestrand remains soft.

In a preferred embodiment of the invention, further pliability andsoftness is endowed the polyfilamentous strand by subjecting it, aftercooling, to repeated flexion in order to cause relative movement betweenadjacent filaments of the strand. By this embodiment of the invention,there is produced an unusually soft and pliable strand.

By the term polyfilamentous plastic strand as used herein and in theappended claims is meant a unitary structure of a plurality of plasticfilaments and includes plastic monofilaments and polyfilaments whichhave been twisted, braided, entangled, spun and the like. Illustrativeof such strands are braided and twisted threads, sutures, strings andrope, spun and continuous synthetic filament yarns, etc. Plasticmaterials from which the strands may be made include any of thefiber-forming synthetic material as, for example, polyesters such aspolyethylene terephthalate; polyolefins such as polyethylene,polypropylene, and the like; the acrylics such as polymethacrylate,polyacrylonitrile, etc.; polycarbonates; polyamides such as nylon;cellulose esters; vinyl polymers such as copolymers of viny choride andvinyidene chloride and coploymers and vinyl chloride and vinylacetate;and like fiberforming plastic materials.

The oils employed in the method of the invention are oils of lubricatingviscosity, stable toward the high hotstretching temperatures to whichthe polyfilamentous strand is subjected and include mineral andsynthetic oils. Generally, such oils have viscosities from about 35 to250 SUS at 210 F. In the case of polyfilamentous surgical sutures, theoil selected from the impregnation should, of course, be physiologicallyinert.

The mineral oils may be solvent-extracted or solventrefined mineral oilsobtained in accordance with conventional methods of solvent refiningpetroleum lubricating oils. The base oil from which these lubricatingfractions are obtained may be derived from parafiinic, naphthenic,asphaltic or mixed base crudes.

Synthetic oils which may be used include those of the ester type, forinstance, the complex esters, diesters, monoesters and polyesters,prepared from aliphatic or aromatic acidic and alcoholic compounds.Various useful ester base oils are disclosed in U.S. Pat. Nos. 2,499,-983; 2,499,984; 2,575,195; 2,575,196; 2,703,811; 2,705,- 724; and2,723,286. Generally, the synthetic base oils consist essentially ofcarbon, hydrogen and oxygen, i.e. the essential nuclear chemicalstructure is formed by these elements alone. However, these oils may besubstituted with other elements such as halogens, e.g. chlorine andfluorine. Some representative components of ester lubricants are ethylpalmitate, ethyl stearate, di-(Z-ethylhexyl) sebacate, ethylene glycoldi-laurate, di-(2-ethylhexyl) phthalate, di (1,3 methylbutyl) adipate,di-(2- ethylbutyl) adipate, di (1 ethylpropyl) adipate, diethyl oxylate,glycerol tri-n-octoate, dicyclohexyl adipate, di- (undecyl) sebacate,tetraethylene glycol di (ethylene hexoate), dicellosolve phthalate,butyl phthallyl butyl glycolate, di-n-hexyl fumarate polymer, di-benzylsebacate and diethylene glycol bis (2 n butoxy ethyl carbonate).2-ethylhexyl-adipate-neopentyl glycyl-adipate-Z- ethylhexyl is arepresentative complex ester.

Preferred synthetic oils are the silicone oils of lubricating viscosity.The silicone oils are liquid organic siloxane polymers in which thesiloxane structure, fi9i-Ofi9i, occurs successively along the polymerchain and in which the major number of residual valences of the siliconeatoms are not satisfied by the substitution thereon of monovalentorganic essentially hydrocarbon radicals such as aromatic and aliphaticradicals. For the purpose for which such silicone oils are used in thepresent invention, the aliphatic substituents of the polymers arepreferably low molecular weight alkyl radicals (i.e., those not havingmore than about carbon atoms per radical) such as methyl, ethyl andbutyl radicals, and the aromatic substituents are preferably phenyl,halogen-substituted phenyl radicals, and alkyl-substituted phenylradicals in which the alkyl group is halogenated. The aromatic siloxanepolymers are preferably those in which a major proportion of thesilicone atoms are bonded to aliphatic radicals such as methyl radicals,and in which the remaining number of organic radicals are aromaticradicals. Typical examples of specific silicone oils which may be usedare the dimethyl siloxane polymers having a viscosity of at leastcentistokes at 25 C. (77 F.) and preferably a viscosity of at least 20centistokes at 25 C. Such methyl-substituted siloxanes are commerciallyknown as the Dow Corning Silicone Type 200 fluids and are mixtures ofpolymers of the homologous series of trimethyl end-blocked dimethylsiloxane polymers having a viscosity at 25 C. ranging up to about 12,500centistokes. Other suitable siloxane polymers which may be used inaccordance with the present invention are the aliphaticandaromatic-substituted siloxane polymers such as the methyl phenylsiloxane polymers of medium aromaticity commercially available as DowCorning DC-SOO silicone oil, and those containing a low ratio of phenylto methyl groups commercially available as Dow Corning DC-SlO siliconeoils. Further examples of suitable aliphaticand aromatic-substitutedsiloxane polymers are the methyl phenyl siloxanes in which the phenylradical is substituted with halogen such as in methyl-p bromophenylsiloxane polymer, methyl-pchlorphenyl siloxane polymer, methyl mtrifluoromethyl phenyl siloxane polymer and methyl 3,4-dichlorophenylsiloxane polymer. It is within the scope of the present invention toemploy any admixture of the above-mew tioned silicone oils as aningredient of the presently described novel compositions.

It is to be understood that the term siloxane polymer as used hereinincludes silicone oils having the following general formula:

LR J. l.

wherein R R and R are the same or different hydrocarbon radicals such asstraight or branched chain alkyl, aryl, alkaryl, arylalkyl,halogen-substituted aryl or halo gen-containing alkyl-substituted arylradicals and n is an integer of at least 2. Such silicones are alsoreferred to in the literature as organo polysiloxanes.

impregnation of the polyfilamentous strands may be effected in anyconvenient manner, for instance, by simply immersing the strand in theoil for a short period of time suflicient to saturate and thoroughlyimpregnate and coat the strand. Ordinarily, complete saturation iseffected in a matter of minutes.

The hot-stretching step of the invention comprises stretching the strandat a temperature above its glass transition temperature, which willpermit a change in configuration without the introduction of internalstresses. Conveniently, the strand may be heated to its softening point.Tension is applied to the heated strand such that the strand isstretched, for example, up to its breaking point. Elongation of over 10%and particularly from about 20% up to about, but not including, thebreaking point are suitable to reduce the elasticity and memory of thestrand sufliciently. The temperature necessary to reduce or eliminateelasticity and memory is called the heat-setting temperature which isknown for various plastic materials. For instance, in the case ofpolyesters of terephthalic acid, a temperature of 320 F. or above willsuffice, although temperatures of about 390 F. to 450 F. are preferred.

The flexion to which the strand may be subjected after cooling in thepreferred embodiment of the invention may be accomplished, for instance,by subjecting the strands to repeated flexion as described in US. Pat.No. 3,257,702 hereby incorporated by reference. Alternatively andpreferably, the fiexion may be induced by passing the impregnated strandunder tension after hot-stretching and cooling over a plurality of sharpedges, each edge being positioned to efliect at least about a 30 changein direction of the passing strand. Treatment of the hot-stretchedstrand in this manner induces a consistent flexing uniformly throughoutthe entire strand. There is consequently provided a strand ofparticularly improved softness and pliability since no area of thisstrand escapes flexing. In addition, the improvement of the inventionoffers reproducibility advantages since it enables repeated preparationof strands of like softness and pliability. Furthermore, the improvedmethod of the invention permits easy adjustment of the degree and therapidity of flexion applied so as to enable optimization of conditionswith respect to whatever type strand is being flexed.

The edge over which the strand is passed may be any suitable elementhaving a relatively sharp edge. By sharp edge as used in thespecification and claims is meant an edge that provides a sharp flex tothe strand over which it is passed in accordance with the methods of theinvention that breaks free or loosens adhering or cohering filaments ofthe strand. Thus, the edge of the element, over which the strand ispassed, should not be so sharp as to cause severing, cutting, orabraiding of the strand; nor should the edge have a radius of curvatureso large as not to provide the desired sharp flex. Included within thesharp edges contemplated by the method of the invention are sharpangular elements which can be considered as having essentially a zeroradius of curvature and cylindrical elements having a very small radiusof curvature of say up to inch as is found in edges having a diameter ofup to ,5 inch. The sharp edged-elements over which the strand is passedmay be constructed out of any suitable solid, hard material resistant towear such as steel, ceramic and the like. The number of edges in theseries over and around which the strand passes will vary depending uponthe nature of the particular polyfilamentous strand, the tensionapplied, and the rate at which the strand is drawn around the elements.Use of too many edges in the series, however, should be avoided since anexcess of edges will often cause the strand to break. A series of threeedges has been found to provide satisfactory results.

Any arrangement of the edges that provides the desired degree in changeof direction can be employed. Although an arrangement which gives a 30change of direction as the strand passes around each edge providessuificient flexion, an arrangement which effects at least about a changeis preferred. The rate at which the strands are passed around the edgeis not critical and, during passage, the strand may be drawn eitherpartially around or completely around each of the elements as long as itis passed over the flex-inducing edge. The strands should be undersufiicient tension as they are passed over the edges in order to inducethe desired flex. Any tension which keeps the strand taut withoutbreaking the strand can be employed. Tensioning devices known to the artmay be used for this purpose, if desired. The drawing of the strand maybe accomplished manually or, if desired, any suitable automatic ormechanical means may be employed. It may be necessary to repeat thepassage of the thread around the plurality of edges to achieve thedesired degree of softness and pliability.

Removal of the oil of lubricating viscosity from the final product maybe effected by any of the techniques well known to the art. For example,the oil may be conveniently removed by washing the product with asuitable solventvfor the oil. The particular solvent selected willdepend upon the lubricating oil employed. For instance, in the case ofthe silicone oils and ester-type synthetic lubricants, suitable solventsinclude, for example, the alkyl and aryl monoethers of alkylene glycolssuch as ethylene glycol, propylene glycol, etc. Illustrative of thesesolvents are those of the Dowanol series. In the case of minerallubricating oils, on the other hand, the aromatic solvents includingbenzene, xylene, toluene and the like are satisfactory.

After extraction of the lubricant from the strand, the strand iswater-washed in any convenient manner and then while still wetimpregnated with inert, insoluble synthetic polymeric particles smallenough to penetrate into the interstices of the strand. The inert,polymeric particles may be any of those known in the art for endowingpolyfilamentous strands with improved softness and flexibility such asthose disclosed in US. Pat. Nos. 3,390,681 and 3,322,125, herebyincorporated by reference. Other suitable inert, insoluble syntheticresins which can be used include polyolefins such as polyethylene,polypropylene and the like; diolefins such as polymers of butadiene andisoprene; polystyrene; polyamides and silicone waxes such as aredisclosed by US. Pat. 3,187,752, hereby incorporated by reference. Aparticularly preferred particle is polytetrafluoroethylene (Teflon).Aqueous dispersions of these materials such as aqueous dispersions ofTeflon described in Berry, US. Pat. No. 2,478,229, are suitable toincorporate the particles into the strands. Saturated aqueousdispersions are particularly suitable. Ordinarily, the inert particlesemployed will have a particle size of up to 1 micron.

If desired, the strand may also be subjected to any of the conventionaltreatments known in the art. For instance, the polyfilamentous strandmay be provided with polytetrafluoroethylene to improve knottability andflexibility 5's described in U.S. Pat. Nos. 3,390,681 and 3,322,- 125.

The following example is included to further illustrate the presentinvention. In the example, reference is made to the attached figureswherein:

FIG. 1 is a perspective view of an apparatus for eflecting the flexingin accordance with a preferred embodiment of the invention and,

FIG. 2 is an enlarged perspective view of one of the sharpedged-elements employed in the apparatus of FIG. 1.

EXAMPLE A five/zero polyethylene terephthalate thread is immersed insilicone fluid (Dow Corning 710 a polyphenylsiloxane having an averagemolecular weight of 2600, approximately 20 silicon atoms per molecule,and a phenyl to methyl ratio of 1.0) for approximately one minute. Theexcess silicone fluid is wiped off the thread and the thread isstretched at approximately 390 F. to an elongation of approximately 50%.The hot-stretched thread is drawn from a supply 1 and manually threadedthrough an introductory guide 3, entrance opening 5, over the wick 7 ofapplicator indicated generally as 9, thropgh exit opening 11, and aroundguides 13, 15 and 17, respectively, in the manner illustrated in FIG. 1.The thread is then attached to take-up spool 9. The guides, eachcontaining a sharp ceramic edge shown, for instance, in FIG. 2 as 19,are arranged in a manner which will effect at least a change ofdirection of the passing thread at each edge. The applicator 9 iscomposed of a container 21 provided with wick 7 and a guide structure 23provided with the aforementioned entrance opening 5 and exit opening 11.The wick 7 is immersed in a cooling medium such as water. When take-upspool 9 is rotated, the hot-stretched thread is pulled over wick 7 ofthe applicator 9 where it is cooled by the application of the liquidcooling medium and then over the sharp edges of guides 13, 15 and 17.

The silicone fluid is then removed from the thread by washing withDowanol 508 (dipropylene glycol monomethyl ether) after which the threadis water-washed. The water-washed thread is gathered into a skein andimmersed before it has had a chance to dry into an aqueous solution ofTeflon. Du Pont blend 2510, containing water and about 58% by weight ofTeflon (polytetrafluoroethylene) particles having an average particlesize of 0.5 micron diluted with water to a concentration, is used. Asurfactant Triton X-lOO, an alkylaryl polyether alcohol having thegeneral formula R(O-CH -CH OH where R is an alkylaryl radical and n isan integer from 5 to or more (Rohm and Haas) and agitation are used tokeep the blend well dispersed.

The skein of thread is kept immersed in the Teflon dispersion for 15minutes to permit the particles of Teflon lubricant to permeate into theinterstices of the thread. While the immersion time can vary widely, ithas been found that 15 minutes is adequate for skeins weighing up to 50pounds as determined by measuring the amounts of Teflon picked up afterfinal processing. Excess Teflon is then removed to provide a threadwhich is extremely pliable and has knotting characteristicssubstantially identical to that of silk sutures.

It is claimed:

1. A method for fabricating a braided polyester suture of improvedsoftness and pliability which comprises thoroughly impregnating abraided polyester suture having elastic memory with a lubricating oilwhich is physiologically inert and is inert with respect to the suture,stretching the impregnated suture while maintaining the suture at theheat-setting temperature above the glass transition temperature of thepolyester to reduce the clastic memory thereof, contacting the stretchedsuture with a solvent for said oil to remove said oil from the suture,water-washing the solvent-treated suture, and impregnating thewater-washed suture while wet with water from the water washing stepwith inert, synthetic, polymeric particles of a resin selected from thegroup consisting of polyolefins, polystyrene, polyamides, siliconewaxes, and polytetrafluoroethylene, said particles having a sizesufliciently small to enter into the interstices of said braided suture.

2. The method of claim 1 wherein the lubricating oil is a siliconefluid.

3. The method of claim 1 wherein the inert, synthetic, polymericparticles are polytetrafluoroethylene.

4 The method of claim 1 wherein the stretched suture is subjected torepeated flexion to cause relative movement between adjacent filamentsof the suture.

5. The method of claim 4 wherein the repeated flexion is effected bypassing the suture under tension over a plurality of sharp edges, eachedge being positioned to eflect at least about a 30 change in directionof the passing strand.

6. The method of claim 5 wherein a series of three edges a e employed.

7. The method of claim 5 wherein each edge effects at least about a 90change in direction of the passing strand.

sharp edge of a guide pin.

Strohmaier et a1. 264-290 N FOREIGN PATENTS Great Britain 264-210 ROBERTF. WHITE, Primary Examiner I. B. LOWE, Assistant Examiner U.S. C1. X.R.

28-75 R; 117-7, 138.8 F, 139.5 A, 161 UZ; 128- 7 8. The method of claim7 wherein each edge is the 3,113,369 3,140,957 3,257,702 ReferencesCited 3,3 4,2 9 UNITED STATES PATENTS 5 7/1964 Tanabe et a1 -7 117-65/1970 Strohmaier et a1. 264-290 N 6/1966 Kurtz 28-72 12/1963 Barrett atal. 28-75 10 19694596 1/1968 Campbell -1 264-290 8/1963 Heighten 264-290T 7/1969 Amok! 264-210 F 4/1968 Kurtz 12s 33s.s 11/1960 K161 2s 72.13 158/1963 Heighten 264-290 11/1963 Bergeijk 61 a1 264-210 F 335.5; 264-233,290 T, DIG 73

